Metal cans, glass bottles and various plastic containers have heretofore been used as packing containers. Among them, plastic containers have been used for a variety of applications from the standpoint of their small weight, shock resistance and cost.
However, though the metal cans and glass bottles permit no oxygen to pass through the container walls, the plastic containers permit oxygen to pass through the container walls to an extent that is not negligible causing a problem from the standpoint of preserving the content.
To enhance the preservation property of the contents, there have been used packing containers using a gas-barrier resin preventing the permeation of oxygen from the exterior in combination with an oxygen-absorbing material that traps oxygen remaining in the container.
Presence of water is essential for the oxygen-absorbing reaction of an iron-type oxygen absorber that is usually used as an oxygen-absorbing material, and iron reacts with water to generate hydrogen. Here, hydrogen that is generated may cause the packing material to become rugged, swollen or ruptured.
Various prior technologies have been proposed to suppress the generation of hydrogen from the oxygen absorber. JP-A-2000-248111 proposes a technology for adding an alkaline substance which is sparingly soluble in water to an oxygen absorber, and JP-A-2000-279147 proposes a method of heat-treating the oxygen absorber.